Dielectric ceramic composition

ABSTRACT

There is provided a dielectric ceramic composition which comprises (Pb,La)(Zr,Ti)O3 and Pb(Mg1/3Nb2/3)O3 in the ratio defined by the formula below. x(Pb1-uLau)(Zr1-vTiv)O3.(1-x)Pb(Mg1/3Nb2/3)O3 wherein 0.10&lt;/=u&lt;/=0.28 0.25&lt;/=v&lt;/=1.00 0.03&lt;/=x&lt;/=0.

FIELD OF THE INVENTION AND RELATED ART STATEMENT

The present invention relates to a dielectric ceramic composition, andmore particularly it is concerned with a ceramic composition having ahigh dielectric constant, high insulation resistance, and highcapacitance-resistance product, which is capable of sintering at a lowtemperature.

Heretofore, the high-dielectric ceramic composition has been dominatedby the one composed mainly of barium titanium (BaTiO₃). The BaTiO₃-based composition generally contains a shifter to shift the Curie pointto the vicinity of room temperature, a depressor to improve thecapacitance-temperature characteristics, a sintering promoter, and ananti-reducing agent.

Examples of the shifter include BaSnO₃, BaZrO₃, CaZrO₃, CaSnO₃, SrTiO₃,PbTiO₃, La₂ O₃, and CeO₂. Examples of the depressor include CaTiO₃,MgTiO₃, Bi₂ (SnO₃)₃, Bi₂ (TiO₃)₃, NiSnO₃, MgZrO₃, and MgSnO₃. Examplesof the sintering promoter include Al₂ O₃, SiO₂, ZnO, CeO₂, B₂ O₃, Nb₂O₅, and WO₃. Examples of the anti-reducing agent include MnO₂, Fe₂ O₃,and CuO.

The composition composed mainly of barium titanate has somedisadvantages. For example, the high sintering temperature (1300° to1400° C.) constitutes a drawback to the sintering operation. Thenecessity of using a high-melting noble metal such as Pd and Pt for theinternal electrodes constitutes another drawback to cost reduction. Thisis true of the case where the composition is applied to layer-builtcapacitors.

For reasons mentioned above, there has been a demand for a dielectricmaterial for layer-built capacitors capable of sintering at a lowtemperature which will permit the internal electrodes to be made of aninexpensive silver-based material. It will contribute to the reducedproduction cost of layer-built capacitor.

OBJECT AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ceramiccomposition capable of sintering at a low temperature which has a highdielectric constant, high insulation resistance, and highcapacitance-resistance product.

It is another object of the invention to provide a ceramic compositionwhich can be made at a low cost into small-sized large-capacitycapacitors of high reliability.

This object is achieved by a dielectric ceramic composition whichcomprises (Pb,La)(Zr,Ti)O₃ and Pb(Mg_(1/3) Nb_(2/3))O₃ in the ratiodefined by the formula below.

    x(Pb.sub.1-u La.sub.u)(Zr.sub.1-v Ti.sub.v)O.sub.3.(1-x)Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3

wherein

0.10≦u≦0.28

0.25≦v≦1.00

0.03≦x≦0.50

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The dielectric ceramic composition of this invention contains(Pb,La)(Zr,Ti)O₃ and Pb(Mg_(1/3) Nb_(2/3))O₃. The ratio of thecomponents is defined by the formula (I).

    x(Pb.sub.1-u La.sub.u)(Zr.sub.1-v Ti.sub.v)O.sub.3.(1-x)Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3                                        (I)

wherein

0.10≦u≦0.28

0.25≦v≦1.00

0.03≦x≦0.50

The ceramic composition of this invention may contain, in addition tothe above-mentioned components, Pb(Fe_(2/3) W_(1/3))O₃ in an amount of 0to 9 mol%, preferably 0 to 8 mol%, and at least one member selected fromthe group consisting of Pb(Mg_(1/2) W_(1/2))O₃, Pb(Ni_(1/2) W_(1/2))O₃,and Pb(Fe_(2/3) W_(1/3))O₃ (excluding the case of Pb(Fe_(2/3) W_(1/3))O₃alone) in an amount of less than 5 mol%, preferably 0 to 4 mol%, intotal.

The ceramic composition of this invention should contain the componentsin the specified ratio for reasons given below.

If the value of u defined in the formula (I) above is less than 0.1, theresulting composition is low in insulation resistance andcapacitance-resistance product; and if it is higher than 0.28, thecomposition decreases in Curie point and dielectric constant. Thus thevalue of u should be in the range of 0.10 to 0.28 both inclusive, andpreferably in the range of 0.10 to 0.25 both inclusive.

If the value of v defined in the formula (I) above is less than 0.25,the resulting composition is high in sintering temperature. Thus thevalue of v should be in the range of 0.25 to 1.00 both inclusive, andpreferably in the range of 0.30 to 1.00 both inclusive.

If the value of x defined in the formula (I) above is less than 0.03,the resulting composition is low in insulation resistance andcapacitance-resistance product; and if it is greater than 0.50, theresulting composition has a low dielectric constant. Thus the value of xshould be in the range of 0.03 to 0.50 both inclusive, and preferably inthe range of 0.03 to 0.40 both inclusive.

If the composition of the invention contains at least one memberselected from the group consisting of Pb(Fe_(2/3) W_(1/3))O₃,Pb(Mg_(1/2) W_(1/2))O₃, and Pb(Ni_(1/2) W_(1/2))O₃, it has a lowsintering temperature.

If the composition contains Pb(Fe_(2/3) W_(1/3))O₃ alone in an amountmore than 9 mol% or if the composition contains either Pb(Mg_(1/2)W_(1/2))O₃ or Pb(Ni_(1/2) W_(1/2))O₃, or two or more members selectedfrom the above-mentioned group in an amount more than 5 mol% (in totalin the case of two or more members), it has a low dielectric constant,which is undesirable.

The dielectric ceramic composition of this invention as defined above isproduced in the following manner. At first the raw material powders suchas lead oxide, lanthanum oxide, zirconium oxide, titanium oxide,magnesium oxide, and niobium oxide are weighed according to a prescribedratio. They are thoroughly mixed using a wet ball mill. The resultingmixture is dried and, if necessary, calcined at 700° to 850° C. Thiscalcination is not a must; but it makes the particles uniform andimproves the dielectric properties. The calcined raw material powder ispulverized further with a wet ball mill, dried, and granulated with abinder such as polyvinyl alcohol. The granules are press-formed into adesired shape, followed by firing. The firing is performed at 1000° to1200° C. for several hours.

The dielectric ceramic composition of this invention which is defined asmentioned above has a high dielectric constant, a high insulationresistance, a high capacitance-resistance product, and a low dielectricloss. Because of these outstanding characteristic properties, thedielectric ceramic composition can be made into small-sizedhigh-capacity ceramic capacitors of high reliability.

In addition, the dielectric ceramic composition of this inventioncontributes to the reduced production cost of layer-built ceramiccapacitors because it can be fired at a low temperature. The firing at alow temperature permits the internal electrodes of layer-built ceramiccapacitors to be made of a comparatively inexpensive silver-basedmaterial.

The invention is now described in more detail with reference to thefollowing examples, which are not intended to limit the scope of theinvention.

EXAMPLE 1

Dielectric ceramic compositions were prepared from PbO, La₂ O₃, ZrO₂,TiO₂, MgO, Nb₂ O₅, NiO, Fe₂ O₃, and WO₃ as the raw materials. Theirmixing ratio defined by the values x, u, and v in the formula (I) isshown in Table 1. The weighed raw materials were mixed with a wet ballmill for 20 hours. The resulting mixture was dehydrated, dried, andcalcined at 750° C. for 2 hours. The calcined mixture was pulverizedagain with a wet ball mill for 20 hours, followed by dehydration anddrying.

After mixing with an organic binder, the resulting powder wascompression-molded into disks, 16 mm in diameter and 0.8 mm thick, undera pressure of 3 tons/cm². The greenware was fired in a magnesia ceramicvessel for 1 hour at a firing temperatures in the range of 1000° to1140° C. as shown in Table 1.

The resulting dielectric disks were examined for electrical properties,with silver electrodes formed by firing at 700° to 800° C. on both sidesof each sample. The results are shown in Table 1.

The dielectric constant and dielectric loss were measured with a YHPdigital LCR meter, Model 4274A, at a frequency of 1 kHz and a voltage of1.0 V_(rms). The insulation resistance was measured with a YHPinsulation resistance tester, Model 4329A, at 100 V for 1 minute.

Incidentally, symbols A, B, and C in Table 1 represent Pb(Fe_(2/3)W_(1/3))O₃, Pb(Mg_(1/2) W_(1/2))O₃, and Pb(Ni_(1/2) W_(1/2))O₃,respectively.

                                      TABLE 1                                     __________________________________________________________________________                             Electrical Properties                                Dielectric Ceramic Composition                                                                    Sintering               Capacitance-                      Sample                                                                            Values in Formula I                                                                      others                                                                             tempera-                                                                           Dielectric                                                                          Dielectric                                                                          Insulation                                                                           resistance                        No. x   u  v   mol %                                                                              ture (°C.)                                                                  constant                                                                            loss (%)                                                                            resistance (Ω)                                                                 product (MΩ ·                                                  μF)                            __________________________________________________________________________     1* 0   -- --       1080 5540  0.31  1.6 × 10.sup.11                                                                1160                               2* 0.03                                                                              0  1.00     1080 8170  0.58  0.9 × 10.sup.11                                                                 980                               3  0.05                                                                              0.20                                                                             1.00     1080 7610  0.27  2.1 × 10.sup.11                                                                2140                               4* 0.05                                                                              0.40                                                                             1.00     1080 5270  0.41  3.5 × 10.sup.11                                                                2420                               5* 0.15                                                                              0.07                                                                             1.00     1080 8360  6.30  0.8 × 10.sup.11                                                                 890                               6  0.15                                                                              0.13                                                                             1.00                                                                              B = 3                                                                              1080 11350 1.82  2.3 × 10.sup.11                                                                3490                               7  0.15                                                                              0.13                                                                             1.00                                                                              C = 3                                                                              1030 8300  0.56  2.2 × 10.sup.11                                                                3560                               8  0.15                                                                              0.13                                                                             1.00                                                                              A = 5                                                                              1030 12410 0.50  2.4 × 10.sup.11                                                                5800                               9  0.15                                                                              0.20                                                                             1.00     1080 7750  0.38  4.5 × 10.sup.11                                                                4660                              10  0.25                                                                              0.20                                                                             1.00     1100 8590  0.55  2.0 × 10.sup.11                                                                2300                              11  0.25                                                                              0.28                                                                             1.00     1100 6100  0.60  6.5 × 10.sup.11                                                                5300                               12*                                                                              0.25                                                                              0.32                                                                             1.00     1100 4530  0.50  7.5 × 10.sup.11                                                                4550                              13  0.35                                                                              0.23                                                                             1.00                                                                              A = 2                                                                              1100 7200  1.06  2.4 × 10.sup.11                                                                2310                              14  0.35                                                                              0.23                                                                             1.00                                                                              B = 1                                                                              1070 6610  0.58  2.5 × 10.sup.11                                                                3220                              15  0.35                                                                              0.23                                                                             1.00                                                                              C = 2                                                                              1070 6420  0.43  2.7 × 10.sup.11                                                                3380                              16  0.35                                                                              0.26                                                                             1.00     1100 6200  1.01  3.7 × 10.sup.11                                                                3070                               17*                                                                              0.50                                                                              0.08                                                                             1.00     1100 4260  5.35  0.7 × 10.sup.11                                                                 400                              18  0.50                                                                              0.20                                                                             1.00     1100 6320  0.62  2.5 × 10.sup.11                                                                2110                               19*                                                                              0.60                                                                              0.15                                                                             1.00     1100 4810  1.80  1.2 × 10.sup.11                                                                 770                              20  0.03                                                                              0.13                                                                             0.85     1100 7230  0.32  2.2 ×  10.sup.11                                                               2130                              21  0.10                                                                              0.10                                                                             0.65     1100 7110  0.84  2.8 × 10.sup.11                                                                2660                              22  0.10                                                                              0.10                                                                             0.65                                                                              B = 2                                                                              1080 6580  0.50  2.7 × 10.sup.11                                                                3460                              23  0.10                                                                              0.10                                                                             0.65                                                                              C = 2                                                                              1100 6390  0.42  2.8 × 10.sup.11                                                                3480                              24  0.10                                                                              0.10                                                                             0.65                                                                              A = 9                                                                              1000 6080  0.27  3.0 × 10.sup.11                                                                3550                              25  0.15                                                                              0.20                                                                             0.65     1100 6210  0.28  3.9 × 10.sup.11                                                                3240                              26  0.40                                                                              0.15                                                                             0.65     1120 6820  0.62  3.4 × 10.sup.11                                                                3110                              27  0.10                                                                              0.10                                                                             0.25     1120 7130  0.58  2.3 × 10.sup.11                                                                2190                               28*                                                                              0.15                                                                              0.33                                                                             0.25     1140 5200  0.32  6.2 × 10.sup.11                                                                4310                               29*                                                                              0.30                                                                              0.08                                                                             0.25     1120 4870  4.80  0.8 × 10.sup.11                                                                 520                              30  0.30                                                                              0.12                                                                             0.25     1140 9600  0.50  4.0 × 10.sup.11                                                                5130                              31  0.30                                                                              0.12                                                                             0.25                                                                              B = 2                                                                              1100 7200  0.51  2.4 × 10.sup.11                                                                3020                              32  0.30                                                                              0.12                                                                             0.25                                                                              B = 5                                                                              1080 6100  0.22  3.9 × 10.sup.11                                                                4580                              33  0.30                                                                              0.12                                                                             0.25                                                                              C = 2                                                                              1100 7040  0.61  3.3 × 10.sup.11                                                                4390                              34  0.30                                                                              0.12                                                                             0.25                                                                              C = 5                                                                              1080 6050  0.26  4.2 × 10.sup.11                                                                4610                              35  0.30                                                                              0.12                                                                             0.25                                                                              A = 5                                                                              1080 8310  0.32  4.0 × 10.sup.11                                                                4620                              36  0.50                                                                              0.10                                                                             0.25     1140 6320  2.67  2.0 × 10.sup.11                                                                2110                              __________________________________________________________________________     *Comparative Examples                                                    

It is to be noted from Table 1 that the dielectric ceramic compositionsdefined by the invention have a high dielectric constant, a highinsulation resistance, a high capacitance-resistance product, and a lowdielectric loss, which are desirable for ceramic capacitors. Inaddition, the dielectric ceramic composition is capable of sintering ata low temperature. The sintering temperature can be lowered further bythe incorporation of Pb(Fe_(2/3) W_(1/3))O₃, Pb(Mg_(1/2) W_(1/2))O₃,and/or Pb(Ni_(1/2) W_(1/2))O₃, without any adverse effect on insulationresistance.

What is claimed is:
 1. A dielectric ceramic composition which comprises(Pb,La)(Zr,Ti)O₃ and Pb(Mg_(1/3) Nb_(2/3))O₃ in the ratio defined by theformula below,

    x(Pb.sub.1-u La.sub.u)(Zr.sub.1-v Ti.sub.v)O.sub.3.(1-x)Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3

wherein 1.0≦u≦0.28 0.25≦v≦1.00 0.03≦x≦0.50.
 2. A dielectric ceramiccomposition set forth in claim 1, which further comprises Pb(Fe_(2/3)W_(1/3))O₃ in an amount of up to 9 mol%.
 3. A dielectric ceramiccomposition set forth in claim 1, which further comprises one ofPb(Mg_(1/2) W_(1/2))O₃, Pb(Ni_(1/2) W_(1/2))O₃, Pb(Mg_(1/2)W_(1/2))O₃.Pb(Ni_(1/2) W_(1/2))O₃, Pb(Mg_(1/2) W_(1/2))O₃.Pb(Fe_(2/3)W_(1/3))O₃, Pb(Ni_(1/2) W_(1/2))O₃.Pb(Fe_(2/3) W_(1/3))O₃, andPb(Mg_(1/2) W_(1/2))O₃.Pb(Ni_(1/2) W_(1/2))O₃.Pb(Fe_(2/3) W_(1/3))O₃ inan amount of less than 5 mol% in total.
 4. A dielectric ceramiccomposition set forth in claim 1, wherein the value of u in the formulais defined by 0.10≦u≦0.25.
 5. A dielectric ceramic composition set forthin claim 1, wherein the value of v in the formula is defined by0.30≦v≦1.00.
 6. A dielectric ceramic composition set forth in claim 1,wherein the value of x in the formula is defined by 0.03≦x≦0.40.
 7. Adielectric ceramic composition set forth in claim 2, wherein the amountof Pb(Fe_(2/3) W_(1/3))O₃ is up to 8 mol%.
 8. A dielectric ceramiccomposition set forth in claim 3, wherein the total amount of one ofPb(Mg_(1/2) W_(1/2))O₃, Pb(Ni_(1/2) W_(1/2))O₃, Pb(Mg_(1/2)W_(1/2))O₃.Pb(Ni_(1/2) W_(1/2))O₃, Pb(Mg_(1/2) W_(1/2))O₃.Pb(Fe_(2/3)W_(1/3))O₃, Pb(Ni_(1/2) W_(1/2))O₃.Pb(Fe_(2/3) W_(1/3))O₃, andPb(Mg_(1/2) W_(1/2))O₃.Pb(Ni_(1/2) W_(1/2))O₃.Pb(Fe_(2/3) W_(1/3))O₃ isup to 4 mol%.